


How to Sin

by elirwen



Series: Pornalot 2018 [2]
Category: Merlin (TV)
Genre: Alternate Universe - Modern Setting, Established Relationship, M/M, Plot What Plot/Porn Without Plot, Porn
Language: English
Status: Completed
Published: 2018-10-21
Updated: 2018-10-21
Packaged: 2019-08-05 12:17:34
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 817
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16367639
Author URL: https://archiveofourown.org/users/elirwen/pseuds/elirwen
Summary: Merlin thinks Arthur needs to study for his exam. Arthur disagrees, and he intends to prove he studied enough.





	How to Sin

**Author's Note:**

> Written for week 2 of Pornalot 2018. Theme: Sin.

“You need to study,” Merlin says, evading Arthur’s attempt to set his laptop aside. 

“No, I don’t,” Arthur says, trying a different tactic and lying down next to Merlin’s side, snuggling close. 

“You need to pass that exam,” Merlin says, ruffling Arthur’s hair. “It was your decision to finish your studies now the company is well-established and doesn’t need your everyday presence.”

“I know,” Arthur says, his voice muffled as he doesn’t bother to turn his face away from Merlin’s side. “But that’s not what I meant. I don’t need to study because I’m ready.”

“I find that hard to believe,” Merlin says, his breath hitching a bit as Arthur’s hand moves from simply resting on his knee to stroking his inner thigh. 

“I need to unwind after all that studying,” Arthur says, his fingers inching closer to Merlin’s clothed groin. 

“I’m not sure you deserve it,” Merlin says but sets his laptop on the bedside table. 

“Your lack of trust in my study abilities wounds me,” Arthur says, mock-offended, pops the button on Merlin’s jeans open and slides the zipper open.

“Math has never been your strong subject,” Merlin says and shifts lower on the mattress, initiating a kiss. 

“Ask me something then,” Arthur says in between playful kisses.

“What?”

“I’ll prove myself to you,” Arthur says, dragging his lips down Merlin’s jaw. “Just pick a subject.”

“Hmmm,” Merlin hums as Arthur mouths at his neck. “The sine function,” he says eventually.

“The sine function,” Arthur repeats, pulls away from the kiss. “It’s a trigonometric function of an angle.”

He straddles Merlin’s legs and pushes his T-shirt up. 

“Which means it works with triangles,” Arthur continues, bending down to lick a trail from Merlin’s left nipple to the right, then down to his navel and back to the left nipple again. “But not just any triangles. The right-angled triangles.” 

He traces two new shapes, starting at the nipple, going down to hip bone, then toward the treasure trail, and back up, repeating the same process on the other side. 

“Okay, I believe you,” Merlin says, his voice deep with arousal, sitting up and pulling his T-shirt off.

“I’m not done yet,” Arthur says, pushing him back down, but continuing Merlin’s previous action by divesting him of his jeans and briefs. 

“Sine is a ratio of sides of the right angled triangle. Opposite side of the angle,” Arthur runs his fingers from the treasure trail to each hip bone, “divided by the hypotenuse.” He drags his fingers up Merlin’s torso. “And that’s how you get the sine function of this angle.” He pinches both of Merlin’s nipples, gently rolling the sensitive nubs between his fingers, watching Merlin arch into his touch, lips parted with a quiet moan.

“Now, the graph of the function is an undulating wave,” Arthur says, drawing the sinuous line across Merlin’s chest, stomach, lower belly, until he reaches Merlin’s cock, and wraps his fingers around it. “It moves up,” he slides his hand up, “and down,” his hand follows the words. 

“Up and down,” he keeps repeating as he fists Merlin’s cock, relishing in Merlin’s gasps of pleasure, watching the muscles in his torso flex as he bucks up into Arthur’s hand. 

“Sometimes the waves are wide,” he slows the movement of his hand until a complete stop.

“No, don’t stop,” Merlin whines and Arthur has to press his hips back to the mattress.

“Patience, love,” Arthur says, lowering himself on top of Merlin and kissing him senseless. “If you hold on for a bit longer, the pleasure will be infinite, just like the graph of the sine function.”

“Your dry spell will be infinite if you don’t get naked right the fuck now,” Merlin grumbles. 

“This I find hard to believe,” Arthur says.

“Try me,” Merlin shoots back, tugging at Arthur’s shirt.

Arthur grins at him but complies, quickly shedding his clothes and climbing back on top of Merlin.

“So where were we?” he asks, pressing their cocks together.

“At promises of infinite pleasure I believe,” Merlin says, hooking his leg behind Arthur’s thigh and pulling him closer. “Get back to undulating, my sine function.”

Arthur barks out a laugh but follows Merlin’s order, grinding against Merlin at an increasing pace.

“Gods, yes, fuck, yes!” Merlin chants.

He wraps his arms around Arthur’s body, holding on tight and meeting each of Arthur’s thrusts. Their harsh pants and Merlin’s encouraging pleas fill the room as they chase their orgasms. 

“Fuck, fuck, fuck,” Merlin gasps out, convulsing under Arthur as he comes. “Fuck,” he breathes out once more, the postorgasmic bliss making his limbs go lax. 

Arthur speeds up his thrusts, drives himself harder against the firm plain of Merlin’s stomach. 

“Paint your graph over me,” Merlin whispers into his ear and, while completely ridiculous, it drives Arthur over the edge and he spills his load all over Merlin’s stomach. 

 

***

 

Arthur aces the exam.

**Author's Note:**

> Kudos and/or comments are ♥.


End file.
